From owner-freebsd-hackers@FreeBSD.ORG Thu Oct 21 12:38:30 2010 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id BE84210656A9; Thu, 21 Oct 2010 12:38:30 +0000 (UTC) (envelope-from des@des.no) Received: from smtp.des.no (smtp.des.no [194.63.250.102]) by mx1.freebsd.org (Postfix) with ESMTP id 7A8C98FC14; Thu, 21 Oct 2010 12:38:30 +0000 (UTC) Received: from ds4.des.no (des.no [84.49.246.2]) by smtp.des.no (Postfix) with ESMTP id 7AEFD1FFC34; Thu, 21 Oct 2010 12:38:29 +0000 (UTC) Received: by ds4.des.no (Postfix, from userid 1001) id 56064845D7; Thu, 21 Oct 2010 14:33:49 +0200 (CEST) From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= To: Alexander Best References: <201009161742.24228.tijl@coosemans.org> <201009161619.o8GGJAmv035378@lurza.secnetix.de> <20101018155944.GA12425@freebsd.org> <868w1r92rf.fsf@ds4.des.no> <20101021122110.GA65490@freebsd.org> Date: Thu, 21 Oct 2010 14:33:49 +0200 In-Reply-To: <20101021122110.GA65490@freebsd.org> (Alexander Best's message of "Thu, 21 Oct 2010 12:21:10 +0000") Message-ID: <86zku77mj6.fsf@ds4.des.no> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.2 (berkeley-unix) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Cc: freebsd-hackers@freebsd.org, mav@freebsd.org, Tijl Coosemans , Oliver Fromme Subject: Re: Summary: Re: Spin down HDD after disk sync or before power off X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 21 Oct 2010 12:38:30 -0000 Alexander Best writes: > Dag-Erling Sm=C3=B8rgrav writes: > > No. Where did you get that idea? To repeat what I've said before - > > several times - in this thread, a modern disk drive can handle hundreds > > of thousands of controlled unloads but only a few hundred emergency > > unloads. Given the choice between "never spin down" and "always spin > > down", the safe alternative is "always spin down". > atacontrol(8) says that: > > "You should not set a spindown timeout on a disk with / or syslog log= ging > on it as the disk will be worn out spinning down and up all the time= ." > > this seems to indicate that spinning down a disk has quite an impact. The problem with setting a short idle timeout is that, on a typical laptop or desktop system, you end up spinning the disk down and back up several hundred times a day, which increases power consumption, I/O latency and wear. However, a single emergency unload (what happens when the disk loses power without first unloading the head) shortens the disk's life expectancy as much as hundreds or thousands of controlled unloads. Unless you think our users commonly reboot their computers hundreds or thousands of times between each time they cycle the power, the safe alternative is to *always* spin down during shutdown. I truly hope this is the *last* time I have to repeat this. It's really not that hard to understand. DES --=20 Dag-Erling Sm=C3=B8rgrav - des@des.no